Method of preparing cellulose acetate films



A ril 10, 1934. E. s. FARROW ET AL METHOD OF PREPARING CELLULOSE ACETATE FILMS Filed March 18, 1929 gnvewtozf attomug EdwarcLSFarrow SfewarZJCarmw,

UNITED STATES PATENT OFFICE METHOD OF PREPARING CELLULOSE ACETATE FILMS Edward S. Farrow and Stewart J. Carroll, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New York Application March 18, 1929, Serial No. 347,813

Claims. (01. 18-57) This invention relates to cellulose acetate films and particularly to a method of preparing such films.

Cellulose acetate films have been prepared heretofore by coating a surface with a dope includ ing cellulose acetate and a suitable solvent such as acetone. Certain softeners or plastifiers may be introduced to improve the quality of the film. The coating is dried in an oven or drier under uniform temperature conditions andv is finally stripped from the surface. The procedure as described produces films which are generally satisfactory, but the operation consumes considerable time and is otherwise unadapted for economical commercial practice.

It is the object of the present invention to pro vide a more satisfactory method of preparing cellulose acetate films, together with a process of incorporating softeners or plastifiers therein.

We have discovered that the dope prepared by dissolving cellulose acetate in a suitable solvent, either with or without a' softener or plastifier, may be hardened rapidly and efiectively to produce a film when the thin layer on a supporting 5 surface is subjected to the action of suitable agents which are non-solvents for cellulose acetate. The agents more suitable are high-boiling compounds such as diamylphthalate, dibutylphthalate, amylbenzoate, ethylene glycol, tricresyl phosphate and monochloronaphthalene. Other organic compounds of similar character may be employed, but those mentioned are adapted to accomplish the purpose of the invention most effectively.

It is also very surprising that such high boiling compounds although they are non-solvents of the cellulose esters will diffuse into the cellulosic body and appear in the final product. This is not merely a surface eiiect but a penetration throughout the whole body of the material. 00-

' agulation by these high boilers affords, then, a

dual purpose of both congealing the dope and combining it with the plastic inducing agent.

In carrying out the method we prepare a dope by dissolving cellulose acetate in a solvent such as acetone, preferably in the proportions of one 5% to 30%, based on the weight of cellulose acetate, of tricresyl phosphate.

5% to 30%, based on the weight of cellulose acetate, of triacetin.

5% to 30%, based on the weight of cellulose acetate, of monoacetin.

The proportions mentioned are those which give the best results, but they are subject to variation and the limits mentioned are not necessarily definite. I

The dope, including the constituents mentioned, is spread in the form of a thin layer on a suitable polished surface and is immediately submerged in the hardening agent, which may comprise any one of the materials hereinbefore mentioned, or any equivalent thereof. As hereinbefore indicated, the hardening agents are generally high-boiling compounds which are nonsolvents for cellulose acetate.

The coating sets quickly as a film which can be stripped generally from the supporting surface after a submergence of approximately twelve minutes. The time required will, of course, vary with the particular composition and the hardening agent employed. As soon as the film is stripped, it is passed rapidly through a washing bath consisting of a solvent for the hardening agent. Ethyl and methyl alcohols are suitable solvents but ethyl alcohol is preferred. The time required for washing does not exceed one-half to one minute. The film after washing is permitted to dry at somewhat above room temperature i. e., approximately 50 C. The drying may be accelerated by raising the temperature, but a higher temperature, than that indicated is generally undesirable.

The film. prepared by the method as described is clear and transparent andfree from bubbles or other blemishes. It is flexible and is adapted to the usual applications of cellulose acetate films. It may be employed, for example, as a support for light-sensitive emulsions for photographic purposes.

The operation may be conducted in any suitable apparatus, an example of which is illustrated diagrammatically in the accompanying drawing.

Referring to the drawing, 5 indicates a revolving drum which may be rotated slowly by power applied from any suitable source. The dope is prepared and is supplied to the drum from a disposed in a receptacle 8. The speed of rotation is such that the film remains in the bath for a suitable period. As the drum rotates, the film is carried therewith from the bath of hardening agent and may be stripped by a doctor 9. The film may be directed then over a roller 11, into a receptacle 12 containing the washing liquid. It travels thence through rolls 13 which remove the surplus liquid. The film may be conducted then through a drying rack, comprising a succession of rollers, 14 from which it is withdrawn as a dried film ready for commercial use. The film may be rolled upon a suitable drum 15, which may be withdrawn from the apparatus at intervals carrying the finished film.

After operating the above apparatus for some time the solution in receptacle 8 gradually increases in the concentration of the film solvent and decreases in the concentration of the plasticizing agent. It is necessary, therefore, to maintain the amount of plastifier at a sufficiently high value to insure thorough coagulation. This may be accomplished by a constant flow of solvent stripped plastifier into and the contaminated plastifier out of receptacle 8. The flow of plastifier may preferably be counter-current to the movement of the film. Means for doing this is not shown. We have found that if diainyl phthalate be used, the acetone content of the bath may increase to approximately before renewal is necessary.

The exceptional advantages derived from the coagulation of cellulose esters by our process as hereinabcve enumerated are further apparent when ease of solvent recovery, freedom from solvent explosions, and other practical and economical improvements are realized. It is self evident that the recovery of the volatile solvents, by mere distillation from the other high-boiling constituents of the coagulating bath, can be more readily effected than the difficult condensation of solvent vapors from a dilute gaseous vehicle. The less expensive apparatus required for distillation is considerable. Furthermore, the practical elimination of vapor explosions, which is ever present when dopes are coagulated in an air stream, is an advantage of far reaching importance.

Various changes may be made in the details of the procedure, and particularly in the selection of softening agents, plastifiers, and hardening agents, without departing from the invention or sacrificing any of its advantages.

Having thus described our invention, What we claim as new and desire to secure by Letters Patent is:

1. The method of preparing cellulose acetate film which comprises forming a film of cellulose acetate dope on a supporting surface and immersing the film thus supported in a non-aqueous coagulating bath containing at least 75% of a plasticizing agent.

2. The method of preparing cellulose acetate film which comprises forming a film of cellulose acetate dope on a supporting surface and immersing the film thus supported in a non-aqueous coagulating bath containing at least 75% of a high-boiling plasticizing agent.

3. The method of preparing cellulose acetate film which comprises forming a film of cellulose acetate dope on a supporting surface and immersing the film thus supported in a non-aqueous coagulating bath containing at least 75% of a high-boiling plasticizing agent and stripping the film from the support and washing the film with a solvent of the plasticizing agent.

4. The method of preparing cellulose acetate film which comprises forming a film of cellulose acetate dope on a supporting surface and immersing the film thus supported in a non-aqueous coagulating bath containing at least 75% of monochloronaphthalene.

5. The method of preparing cellulose acetate film which comprises forming a film of cellulose acetate dope on a supporting surface and immersing the film thus supported in a non-aqueous coagulating bath containing at least 75% of tricresyl phosphate.

6. The method of preparing cellulose acetate film which comprises forming a film of cellulose acetate dope on a supporting surface and immersing the film thus supported in a non-aqueous coagulating bath containing at least 75% of triacetin.

7. The method of preparing cellulose acetate film which comprises forming a film of cellulose acetate dope containing a plastifier on a supporting surface and immersing the film thus supported in a non-aqueous coagulating bath containing at least 75% of a plasticizing agent.

8. The method of preparing cellulose acetate film which comprises forming a film of cellulose cetate dope on a supporting surface and immersing the film thus supported in a non-aqueous coagulating bath containing at least 75% of monochlornaphthalene, and acetone.

9. The method of preparing cellulose acetate film which comprises forming a film of cellulose acetate dope on a supporting surface and immersing the film thus supported in a non-aqueous coagulating bath containing at least 75% of tricresyl phosphate, and acetone.

10. The method of preparing cellulose acetate film which comprises forming a film of cellulose acetate dope on a supporting surface and immersing the film thus supported in a non-aqueous coagulating bath containing at least 75% of triacetin, and acetone.

STEWART J. CARROLL. EDWARD S. FARROW. 

